1. Technical Field of the Invention
The present invention relates to high capacity valves, and more particularly to a globe valve configured to reduce flow losses and increase fluid flows therethrough.
2. Description of Related Art
In a globe valve, flow between a first fluid passage and a second fluid passage is controlled by a plug movable within a tubular throttling cage. Fluid flowing from the first passage to the second passage flows into the throttling cage through an open end, and out of the throttling cage through a plurality of radially oriented flow ports. Alternately, fluid flowing from the second passage to the first flows into the throttling cage through the radial flow ports and out the open end to the first passage. In either case, the plug is movable to selectively cover the flow ports, thereby restricting flow through the throttling cage and the valve.
The flow path through a globe valve is convoluted. In an example where fluid is flowing from the first passage to the second, fluid passes through the open end and into the throttling cage about its axis. Thereafter, the flow must be diverted 90° to exit through the radially oriented flow ports. Flow out through the radially oriented flow ports exits in all directions (360°) and is collected and directed towards a single passage. Thus, a portion of the flow exiting the radially oriented flow ports is diverted as much as 180° to flow around the interior of the valve to the passage. The directional changes are exacerbated in an inline configuration where the valve inlet and outlet are on a common flow axis, because the throttling cage is positioned in perpendicular relation to the common flow axis. As a result, the flow must be diverted an additional 90° to flow through the open end of the throttling cage. Further, the radial flow ports may not be vertically aligned with the outlet, and thus the flow between the second passage and the flow ports must be diverted to a common axis.
The convoluted flow causes flow losses in areas of the valve that are not controlled by the throttling cage and plug. Not only do the losses limit the overall flow efficiency of the valve, but because they are independent of the flow throttling, the losses impact the characteristics of the throttling control. In other words, as the flow rate increases the total flow loss through the valve becomes more a function of flow rate and less a function of the amount of the flow port covered by the plug.
Prior attempts to reduce flow losses have included increasing the size of the valve body and the fluid ports through which the fluid flows. Unfortunately, larger components such as a larger valve body and a larger throttling cage and plug that would result from the larger fluid ports, also increase the weight and cost of the valve. Further, such larger components also require stronger and more expensive mechanisms, for example the mechanism on which the plug reciprocates. It is preferable that a valve conform to commercially standardized installation dimensions. These dimensions limit the extent to which the size of the valve body and other components can be increased.
Therefore, there is a need for a globe valve that has reduced flow losses, especially at high flow rates, that is comparable in size, weight, and cost to other globe valves.